Vacuum mixing device for bone cement and method for mixing bone cement in said device

ABSTRACT

The application relates to a vacuum mixing device ( 1 ) for bone cement, where the monomer is pressed into a mixing container ( 2 ) due to the surrounding vacuum and a gas volume present in the monomer container ( 10 ).

FIELD OF THE INVENTION

The invention relates to a vacuum mixing device for bone cement and to amethod for producing bone cement.

BACKGROUND OF THE INVENTION

Mixing devices for bone cement are known.

Such a generic mixing device is shown, for example, in the applicant'sGerman patent application DE 10 2007 041 666 A1. When preparing bonecement, a powder, in particular a PMMA powder, is typically mixed with aliquid monomer. Vacuum mixing systems are known so as to avoid theformation of bubbles and/or to prevent harmful gaseous substances thatdevelop during preparation from escaping into the environment. These aresystems in which the mixing container comprises a connection for avacuum hose, via which the container is placed under a vacuum during themixing process.

Known conventional system often require relatively complicatedoperation, in which the user must perform several steps associated withsources of errors. In particular, it is important to precisely adhere tothe predefined mixing ratio between the monomer and powder.

For this purpose, for example, systems are known in which the monomer issuctioned into the mixing container based on a vacuum that is present inthe mixing container. Such conventional systems generally have a valvethrough which air can flow into the monomer container, so that theexisting liquid is completely discharged from the monomer container.Such a system is described, for example, in the European patentspecification EP 0 725 647 B1.

The disadvantage of such a system is that the bone cement can becomecontaminated with microbes from the ambient air, in particular if thissystem is not operated in a sterile environment.

OBJECT OF THE INVENTION

In contrast, it is the object of the invention to at least reduce theaforementioned disadvantages of the prior art.

It is in particular an object of the invention to be able to provide avacuum mixing system for bone cement which enables simple and safehandling.

SUMMARY OF THE INVENTION

The object of the invention is already achieved by a vacuum mixingdevice and by a method for preparing bone cement according to any one ofthe independent claims.

Preferred embodiments and refinements of the invention are disclosed inthe respective dependent claims.

The invention relates first to a vacuum mixing device for bone cement,comprising a mixing chamber in which a monomer can be mixed with thepowder. So as to avoid the formation of bubbles and prevent harmfulgases from escaping, the mixing chamber can be connected to a vacuumsource, in particular to a vacuum pump.

The vacuum mixing device moreover comprises a monomer container, whichcan be coupled to the mixing chamber. The monomer is preferably alreadycontained in the monomer container upon delivery of the vacuum mixingdevice and thus does not need to be withdrawn from a separate containerand added. The term “can be coupled” means that the vacuum mixing devicecomprises means for forming a passage in which the monomer flows fromthe monomer container into the mixing container connected to the monomercontainer.

According to the invention, the closed monomer container is filledpartially with a gas, the volume of which is calculated such that, whena vacuum is present, the monomer is displaced by the gas and thus flowsinto the mixing container.

The monomer container is preferably not subject to over-pressure, butinstead has, for example, substantially atmospheric pressure. Thisenables a simpler design of the container, and the monomer is preventedfrom escaping in an uncontrolled manner in the event of damage.

If the monomer container is, for example, under atmospheric pressure anda vacuum source is applied that generates a vacuum of approximately 0.5bar in the mixing container, the gas volume in the monomer containermust consequently account for at least half the volume.

The invention enables an entirely closed design of the vacuum mixingdevice, so that there is no risk during mixing for microbes from the airthat is suctioned in to contaminate the bone cement.

The gas that is used can be air in the simplest case, but other gases,in particular those that form a preserving protective atmosphere, arealso conceivable. Nitrogen or a noble gas may also be used, for example.

In a preferred embodiment of the invention, the gas volume is so largethat the monomer flows into the mixing container up to a predefined filllevel, or fully, when a vacuum is present.

A predefined residual fill quantity can be determined, for example, bythe height of the cannula protruding into the monomer container duringmixing. Depending on the embodiment, complete emptying of the monomercontainer is also possible.

In this embodiment of the invention, the amount of liquid to bedispensed can be exactly gauged, because the monomer container isemptied fully automatically and the user has no influence on theresidual quantity remaining in the monomer container, as is the case,for example, with filling using a syringe.

In a preferred embodiment of the invention, at least 20%, and morepreferably 40%, of the volume of the monomer container is filled withthe gas.

In a refinement of the invention, the monomer container has a membraneand the vacuum mixing device comprises a piercing cannula, by means ofwhich the membrane can be pierced and the monomer thus flows via thecannula into the mixing container.

This embodiment of the invention enables, in particular, the use ofcommercially available monomer vials made of glass, which are providedwith a membrane. The monomer is thus stored in a safe and sterile mannerin the monomer vial.

The invention further relates to a vacuum mixing device which comprisesa mixing container, which can be connected to a vacuum source. Thevacuum mixing device comprises a monomer container, which can be coupledto the mixing container.

So as to enable a particularly simple design of the device, the monomercontainer is disposed on a handle, which can also be used to actuate amixing blade in the mixing chamber, wherein the monomer can be mixedmanually with the powder using this mixing blade by moving the mixingblade up and down.

A rod is connected to the handle so as to move the mixing blade.

According to the invention, the rod is guided in a plate, which can beused as a plunger for expelling the bone cement after the bone cementhas been prepared.

The rod preferably comprises a channel, which is used to join the mixingcontainer to the monomer container, which is to say to allow the monomerto flow into the mixing container.

The invention enables a design of a vacuum mixing device which isparticularly easy to handle, wherein, as in a preferred embodiment ofthe invention, the handle together with the monomer container can bebroken off after the mixing process is complete and the mixing containeris employed as a kind of cartridge in a dosing gun. To this end, theplate, which initially serves to guide the rod, is used as a plunger forpushing the bone cement out of the mixing container.

According to one embodiment of the invention, the monomer containercomprises a monomer vial disposed in a receiving unit. This embodimentof the invention makes is possible, among others, to use commerciallyavailable monomer vials and, as in a preferred embodiment of theinvention, the remaining monomer container does not have to be designedto be vacuum-sealed because, for example, a membrane that is present onthe monomer vial can served as a sealing element.

In a special embodiment of the invention, the receiving unit is designedto be telescoping. A monomer vial held in the receiving unit can thus bepushed onto a cannula, for example.

The invention further relates to a vacuum mixing device comprising amixing chamber and a monomer container, which can be coupled to themixing chamber.

According to the invention, the monomer container engages in the coupledstate and is preferably locked in this engaged state.

Thus, the user cannot break the connection between the monomer containerand mixing container once it has been established. The monomer thusenters the mixing container completely, and there is no risk of the userseparating the monomer container as a result of improper use before thecontainer is emptied.

In a refinement of the invention, the vacuum mixing device comprises asafety bolt which, upon removal, releases the monomer container formovement into the coupled state. Such a safety container preventsaccidental actuation of the device.

The vacuum mixing device preferably comprises means for blockingreinsertion of the removed safety bolt. Once the safety bolt has beenpulled, it thus also serves as a tamper-proofing element, making itimmediately apparent if the vacuum mixing device has been previouslyused and therefore consumed.

The invention further relates to a method for preparing bone cement. Tothis end, a monomer is mixed with a powder in a mixing container and avacuum is applied to the mixing container, at least while mixing.

According to the invention, when the vacuum is present, the monomer ispressed out of the monomer container into the mixing container by a gasthat expands as a result of the vacuum.

The method makes a fully closed design of the mixing system possible.

During preparation, the mixing cup and monomer container are thuspreferably protected from the penetration of outside air.

In one embodiment of the invention, the monomer container is pierced bymeans of a cannula and the monomer is conducted via the cannula into themixing container.

In this connected position, the monomer container engages such that theinflow of monomer can no longer be interrupted.

In a refinement of the invention, the monomer container is separatedfrom the mixing container after the bone cement has been prepared, andthe mixing container is used as a cartridge for a dosing gun.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail hereafter with referenceto the drawings, these being FIG. 1 to FIG. 6, which show schematicviews of embodiments of the invention.

FIG. 1 to FIG. 4 show schematic views of an exemplary embodiment of ahandle comprising a monomer container for a vacuum mixing deviceaccording to the invention.

The entire vacuum mixing device will be described in more detail withreference to FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a monomer container 10 designed as ahandle for a mixing blade (not shown). The monomer container 10 has asubstantially cylindrical shape and comprises an actuating button 11 forreleasing the monomer (not shown).

In order to be able to press the actuating button 11, a safety bolt 12having a handle 13, which forms a finger hole, is provided, which mustbe removed first.

After the safety bolt 12 has been removed, the actuating button 11 canbe pressed and the monomer flows, with a vacuum in the mixing container,into the mixing container (not shown) via a channel (not shown) that isembedded in the rod 6.

FIG. 2 shows a sectional view of the monomer container 10 shown in FIG.1 in a starting state, which is to say prior to use.

The monomer container 10 comprises a lower housing part 15 and an upperhousing part 16, which is also designed as the actuating button 11.

The housing parts 15, 16 are used to accommodate a commerciallyavailable monomer vial 17 made of glass, which is sealed with a membrane18.

The monomer fills the monomer vial 17 approximately half in thisexemplary embodiment. The fill level is predefined by the line 25.

The monomer container 10 further comprises a cannula 19, which isconnected to a channel 20 that is embedded in the rod 6.

The cannula 19 and the membrane 18 of the monomer vial 17 are held apartfrom each other by the safety bolt 12 so that accidental actuation isnot possible.

The safety bolt 12 comprises a spring-loaded tongue 14 so as tocompensate for manufacturing tolerances of the monomer vial 17.

As soon as the safety bolt 12 has been pulled out, the monomer vial 17slides into a position in which the safety bolt 12 cannot bere-inserted.

FIG. 3 shows a sectional view of the monomer container 10 afteractuation.

When the actuating button is pressed, the upper housing part 16 and thelower housing part 15 are pushed inside each other, whereby the monomervial 17 is pushed onto the cannula 19 which pierces the membrane 18 sothat the monomer can enter the mixing container (not shown) via thechannel 20.

Because of the air volume that is present above the fill level 25 andthe vacuum that is present in the mixing container, the monomer isemptied to a low residual fill level, which is predefined by theposition of the cannula 19.

In order to define an exact position of the cannula 19 relative to themonomer vial 17, a ring 21 is provided in the lower housing part, withthe monomer vial 17 being seated on this ring in the actuated state.

FIG. 4 shows a detail view of the head of the monomer container shown inFIG. 3. The engagement of the monomer container will be described inmore detail with reference to this figure.

The upper housing part comprises catch hooks 22, which in the actuatedstate engage beneath catch lugs 23 of the lower housing part. For thispurpose, the catch hooks 22 are beveled. It is not possible to pull themapart after engagement.

So as to further increase the protection from manipulation, ribs 24 areprovided on the lower housing part, which substantially prevent the useof a tool to push the catch hooks inward from beneath and thus returnthe monomer vial to the original position.

FIG. 5 is a schematic view of the entire vacuum mixing device.

The monomer container 10 is designed as a handle, which is connected viaa rod 6 to a mixing blade (not shown).

The mixing container 2 is preferably already prefilled with the powder.

In order to ensure that the powder does not enter the rod 6, a filter,and more particularly a filter plate, is provided (not shown) at thelower end of the rod.

When the vacuum mixing device 1 is used, a vacuum pump is connected to avacuum connection 3 on the mixing container 2. A nonwoven fabric (notshown) that is embedded in the vacuum connection prevents bone cementfrom escaping.

A withdrawal opening, which initially is still screwed to a base 5, islocated at the bottom of the mixing container 2.

The user (not shown) first connects the mixing container 2 to thevacuum.

Then, he pulls the safety bolt and pushes the actuating button 11 of themonomer container.

Because of the vacuum, the monomer (not shown) is displaced by the gastrapped in the monomer container 10 and flows via the rod 6 into themixing container 2. To this end, the rod 6 comprises lateral openingsabove the mixing blades (not shown).

The user then uses the monomer container 10 as a handle so as to movethe mixing blades (not shown) in the mixing container 2 and thus preparethe bone cement.

Thereafter, the user pulls the mixing blade all the way to the top andcompletely breaks off the rod 6 together with the monomer container 10at a predetermined breaking point.

Moreover, the user unscrews the base 5, whereby the withdrawal openingis uncovered.

The mixing container 2 can now be utilized as a cartridge for a dosinggun (not shown). To this end, the cover 7 of the mixing container 2, inwhich the rod 6 is also guided, serves as a plunger. The cover 7 can,for this purpose, be connected to the remaining mixing container 2 sothat it detaches at a particular force and can then be pushed forward.The cover can, for example, be pressed into a groove of the cylindricalhousing of the mixing container 2.

FIG. 6 shows a further perspective view of a vacuum mixing device 1. Inthis view, the base (5 in FIG. 5) has already been unscrewed, so thatthe withdrawal opening 4 is visible.

The invention enables particularly simple and safe handling of bonecement.

The invention is, of course, not limited to a combination of theaforedescribed characteristics, but a person skilled in the art cancombine all the features to the extent this is expedient.

LIST OF REFERENCE NUMERALS

-   1 Vacuum mixing device-   2 Mixing container-   3 Vacuum connection-   4 Withdrawal opening-   5 Base-   6 Rod-   7 Cover-   10 Monomer container-   11 Actuating button-   12 Safety bolt-   13 Handle-   14 Tongue-   15 Lower housing part-   16 Upper housing part-   17 Monomer vial-   18 Membrane-   19 Cannula-   20 Channel-   21 Ring-   22 Catch hook-   23 Catch lug-   24 Rib-   25 Fill level

1-16. (canceled)
 17. A vacuum mixing device for bone cement, comprisinga mixing container, which can be connected to a vacuum source, and amonomer container, which can be coupled to the mixing container, whereinthe monomer container has a membrane, and the vacuum mixing devicecomprises a piercing cannula via which the monomer flows into the mixingcontainer, wherein the monomer container is filled partially with a gas,so that the monomer flows from the monomer container into the mixingcontainer when a vacuum is present in the mixing container, wherein thegas volume is so large that the monomer flows into the mixing containerup to a predefined fill level, or fully, when a vacuum is present. 18.The vacuum mixing device according to claim 17, wherein at least 20% ofthe volume of the monomer container is filled with the gas.
 19. A vacuummixing device, comprising a mixing container, which can be connected toa vacuum source, and a monomer container, which can be coupled to themixing container, the monomer container being disposed on a handle,which can be used to actuate a mixing blade in the mixing chamber via arod, wherein the rod is guided in a plate, which is used as a plungerfor expelling the bone cement after the bone cement has been prepared.20. The vacuum mixing device according to claim 19, wherein the monomercontainer can be coupled to the mixing chamber via a channel in thehandle.
 21. The vacuum mixing device according to claim 20, wherein thechannel is disposed in a rod for driving the mixing blade.
 22. Thevacuum mixing device according to claim 21, wherein the rod comprises apredetermined breaking point.
 23. The vacuum mixing device according toclaim 22, wherein the monomer container comprises a monomer vialdisposed in a receiving unit.
 24. The vacuum mixing device according toclaim 23, wherein the receiving unit is designed in a telescopingmanner.
 25. The vacuum mixing device according to claim 23, wherein themonomer vial held in the receiving unit can be pushed onto a cannula.26. A vacuum mixing device, comprising a mixing chamber, which can beconnected to a vacuum source, and a mixing container, which can becoupled to a mixing chamber, wherein the monomer container engages inthe coupled state.
 27. The vacuum mixing device according to claim 26,wherein the vacuum mixing device is designed so that the monomercontainer is locked in the engaged state.
 28. The vacuum mixing deviceaccording to claim 26, wherein the vacuum mixing device comprises asafety bolt, which, upon removal, releases the monomer container formovement into the coupled state.
 29. The vacuum mixing device accordingto claim 28, wherein the vacuum mixing device comprises means forblocking reinsertion of the removed safety bolt.
 30. A method forpreparing bone cement, with a monomer being mixed with a powder in amixing container and a vacuum being applied to the mixing container,wherein a monomer container is pierced, the monomer flows via a cannulainto the mixing container and, when a vacuum is present, the monomer ispushed out of the monomer container into the mixing container by a gasthat expands as a result of the vacuum.
 31. The method for preparingbone cement according to claim 30, wherein during preparation, themixing cup and monomer container are protected from the penetration ofoutside air.
 32. The method for preparing bone cement according to claim30, wherein the monomer container engages in a position in which it iscoupled to the mixing device.